Jamie Merrigan says that without the confession wrought from the police tactic he doubts there's enough evidence for another trial.
The Supreme Court of Canada ruled that Nelson Hart's confession during the sting operation cannot be used against him should he face another trial.
Crown prosecutor Frances Knickle (kah-NICK'-al) and provincial Attorney General Felix Collins declined comment while reviewing the top court judgment.
Merrigan says Hart, who had limited education and low income, was an especially vulnerable target for such an aggressive police sting.
The Mr. Big technique involves luring suspects into fake criminal gangs in order to extract confessions to past crimes.
Hart was found guilty of first-degree murder in the 2002 drowning deaths of his three-year-old twins in Gander Lake.